Controllable space current electron discharge tube with magnetic field



y 1952 J. H. BURNETT 4 2,605,437

- CONTROLLABLE SPACE CURRENT ELECTRON DISCHARGE TUBE WITH MAGNETIC FIELD Original Filed Feb. 12. 1946 (Ittorneg Patented July 29, 1952 CONTROLLABLE SPACE CURRENT ELEC TRON DISCHARGE .TUBE WITH MAGNETIC FIELD, I.

James H. Burnett, Upper Montclair, N. J., assignor, by mesne assignments, to General Railway Signal Company, a corporation of New York Original application February 12, 1946, Serial No. 7 647,007. Divided and this application February 2, 1950, Serial No. 142,063

This invention relates to electronic devices,

and more particularly to controllable electron discharge devices suitable for amplifiers. 'oscillators, and the like.

This application is a division of my prior application, Ser. No.'647,007, filed February 12', 1946, for Electron Discharge Devices, now Pat. No. 2,543,739 dated February 27, 1951. p

In the usual type of controllable electron discharge tubes, such as exemplified by the ordinary and well known triode, electrons are attracted to the grid whenever it assumes a positive potential with respect to the cathode; and V theresultant grid current imposes limitations upon the efiicient and effective use of such tubes in various applications. These and other limitations in the efliciency and use of their usual type of grid controlled electron discharge tube,

such tubes clearly increased, if the flow of electrons to the; positive grid can be effectively prevented.

With these considerations'in mind, one of the objects of the present invention is to provide a controllable electron discharge device which may be proportioned-to have the desirable operatingcharacteristics of the usual grid control triode or similar multiple electrode tube, but which does not have any appreciable electron current to the grid or control electrode, even when this grid or control electrode assumes relatively high positive potentials with respect to the cathode.

'A further object of the invention is to attain this desirable objective by a simple and effective structural organization, in which the component parts may be readily proportioned and arranged to obtain any desired rating and operating characteristics.

Various other objects, attributes and characteristic features of the invention will be in part apparent, and in part pointed out, as the nature of the invention and certain specific embodimerits are hereinafter described.

Generally speaking, and without attempting to define the nature and scope of the invention, it is proposed to combine a magnetic field with a cathode, anode, and a control electrode in such a way that, although the control electrode may perform its usual function of controlling the electron space current in accordance with variationsdn-its impressed potential, the electrons 2 claim (01. 313-457) emitted by the cathode and forming the electron or space current are influenced by the magnetic field so as not to reach the control electrode or grid. even though it assumes a relatively high. positive potential with respect to the cathode in theoperation of the tube. 1

Considering the general attributes of the invention from anotheryiewpoint, the control element or electrode, instead of being the conventional grid with spaces between its wires for the passage of electrons and located between the cathode and anode in the path of direct movement of electrons from the cathode to the anode, is disposed to one side of the direct or normal path of electrons emitted by the cathode and attracted to the anode, but in such a position that variations in the. electrostatic field due to potentials on the control electrode may influence the intensity of the electron current and exercise the same controlling function as the grid of the conventional triode; and this arrangement or disposition of cathode, anode and control electrode is supplemented by a magnetic field acting in a direction and with such intensity as to confine the movement of electrons emitted from the cathode into a beam or stream over a discharge path of the appropriate area which does not' of facilitating an explanation and understanding I of the nature of the invention than for the purpose of illustrating the details of any particular structure that may be advantageously employed in practice.

In the embodiment of the invention illustrated, the cathode is in the form of an interrupted ring 20, the control electrodes are cylinder 2|, 22, in-

side and outside of this cathode, and the anodes are circular plates 23, 23 disposed at the ends of the cylindrical control electrodes'2l and .22 in' planes substantially parallel with the plane of the annular cathode 20. The cathode 20 may be a directly heated wire of tungsten or other emissive metal, a wire thoriated or oxide coated, or

a cathode of the indirectly heated type,the particular form of cathode not being material towith a fine nickel wire .to aidadherenceof the. emissive coating and to help in maintaining a uniform temperature. The oxide coating on'this cathode is preferably formed and treated in the manner disclosed in the prior patents to D. V.

Edwards et al., No. 1,985,855, December 25', 1934, Y electronldischar'g'e tube is dependent upon the and No. 2,081,864, May 25, 1937; In the structure illustrated, the cathode 20 is connected to non-emissive supporting rods 24,

25 bent at their upper ends and, extending through an opening in the outer cylindrical control electrode 22, with a suitable insulating bushing (not shown) if desired; and these supporting rods 24, 25 are bent and anchoredfa't their" lower ends in the reentrantstem 26"of the tube enve lope E and connected by leads 27, 28 to terminal pins 29, 36 on the usual bas'e 3| in accordance with the usual tube construction.

The circular plates 23,, 23' Jconstituting, the -anodes are preferably provided with a-central hole 32 170 facilitate heating. of these plates; by induc: tion heating during ,the outgasingprocess, and are connected by a welded .brace 3'4 andsupported by a bifurcated rigid supporting element 35 con-,

nected to a rod 36, which is sealed in the itopof the envelope. E and :connectedtoa terminal cap 26 of the tube adjacent the cathode leads, in

orderto permit the use of higher potentials on the control electrodes with respect to the oathode. I The magnetostatic field as shown is provided by a permanent magnet PM of annular form which is magnetized as indicatedto provide a field directed along the axis of the tube.

After the tube elementshave been mounted in the envelope, which is provided :with the usual exhaust tube, as indicated at 6 6, the. electrodes. supporting elements and envelope are freed'of occluded gases by a suitable baking, inductionh'eat mg and bombardment procedure; 'and' the 'en-' velope is'ltho'r'oughly evacuated'of all jai'r and gases, in accordance'with' recognized practiceto provide wha'tis'knownasa hard tube.

Considering now the function and operation of the controllable electrondischarge tube at this invention, it is found'tha't a disposition ofelectrodes; together with'a magnetic field, such as illustrated and described, provides a control of the electron or spacec'urrent "to theanodes in accordance with the variations in the potential of the control electrodes with respect to the cathode, and that there is no appreciable movement of electrons to the control-electrodes and a resultant electron current, even though the control electrodesla'ssume a relatively high positive potentialiwithrespe'ct'to'the cathode. "Theoretical consideration indic'ates that this action or'performance of the device of this invention may be attributed to- I certain recognized phenomena ,inconnection-fwith the emission and movement of: electrons in discharge i=tubes and in magnetic fields; abut itvsshouldxbeunderstood that the following discussion of a theory of operation is not comprehensive, nor necessarily applicable in all details to the various formswhich the tube ofi'this inventionmnaytake. t

With "regard" to" the controlling effect of the potential on the control electrodes, it may be said that the number of electrons emitted from ,the cathode and attracted to the anodes in an potential gradient to the cathode, and primarily the electrostatic field adjacent the cathode. In the .tube of this invention, the electrostatic field of the exi'sting potential on the control electrodes acts to modify this potential gradient provided by the space charge and anode voltage in such a way'as to control the electron current actually fiowing'tojthe anodes and through the external output circuit. It'may be assumed that the control electrodes of the tube of this invention act in this respect much likethe grid of the conventional triode, negative potentials tending to retive spacing of the elements as wellas the Tvol ages involved, are factors in determining the iritensity of the anode'cur'ren't and the effectiveness a nd"range of control'of the potentials on the control electrodes;

Speaking generally, it is contemplated for ordinary uses of thef'tube that the cathode will be capable of emitting a surplus of "electrons at: the maximum anode operating voltage, so th'a'tthe' anode current is li n' ite'd by space charge effects.

Under such conditions; the anode'current for a given'ano'cl'e voltage increases with a decrease in 'anodeitocatho'de spacing; andjin general the anodefto cathode" spacing may be chosenjfor certain anode voltages toiprcvide the desired an=' ode current. 1 Y

Considering nowfthei'mportant feature of this inventioniof utilizing the magnetic field in a way to-minimize or eliminate; electron current to "the control electrodes at positive potentials, it is afamiliar phenomena that a magnetic field will influence the'path of "movement of an electron.

More specifically, an electron as a negativelyperpendicular to thedirection of the magnetic lines of force.

jected to forces similar" to those acting on acurrent carrying conductor moving in a -mag'-" net1c field; and the same quantitative relations apply. .While an electricfield, such as produced by'voltageslon electrodes in the tube, exerts a force" on an electron whether atrest or in mo tion, and in the directionof the field, a magnetic .field exerts force'on.an electr0n.on1y when itzis.

in-motion, and-in a direction at right angles-to the direction of such magnetic field. Consequently, amagnetic field does not accelerate'or retard the motion ,of an electron under the infiuenceof an-electric field, but .merely changes itsdirection of movement. H

In the embodiment of the invention illustrated, thesunagnet PM macts axially'rof rthe cylindrical:

This force isdependent upon the-strength of the mag-' netic field, andalso'upon the component ofthe instantaneous velocity of the electron which 'is' V In this respect" an electron-in motion in a magnetic field may be saidto be sub control electrodes 2 I, 22; and it can be seen that electrons leaving the surface of the cathode 20 and moving either up or down toward the anode plates 23, 23 are not aifected by the magnetic field and move in straight lines toward such anode under the influence of the electric field of the anode voltage. In the case of electrons leaving the surface of the cathode with a, component of velocity at right angles to the magnetic lines of force, however, such electrons will be deflected by the magnetic field in accordance with well known principles; and since these electrons are subject to the influence of the electric field as well as the magnetic field, they will move in what may be called a spiral path toward one of the anodes. In other words, it may be said that the magnetic field acts to converge or focus the electrons leaving the cathode into a beam or stream directed toward each of the anodes.

Since the tube of this invention involves the influence of a magnetic field upon the electrons moving from the cathode to the anode, it is desirable to avoid any weakening or distortion of this magnetic field by employing nonmagnetic metals for the electrodes and many of the supporting elements. For ordinary purposes it is considered preferable to employ tantalum for the electrodes, on account of the facility with which this metal gives up occluded gases and its tendency to absorb gases given off during operation. Molybdenum, or other nonmagnetic metals of similar characteristics, are preferably employed for the mounting and supporting elements of the tube, except at the glass seals, rather than nickel, commonly employed for such purpose, in order that the magnetic qualities of nickel may not adversely aifect the magnetic flux distribution.

Various adaptations, modifications, and additions may be made to the specific embodiments of the invention illustrated and described without departing from its underlying principles, func-' tions, and mode of operation; and I desire to have it understood that the invention is not limited to the specific structural organizations illus- 6 trated or described, but may take a wide variety of other forms.

What I claim is:

1. An electron discharge tube comprising, a circular filamentary thermionic emissive cathode, concentric cylindrical control electrodes disposed inside and outside of said cathode with their axes substantially at right angles to the plane of said cathode, anode plates disposed on opposite sides of said cathode beyond the ends of said control electrode in planes substantially parallel with the plane of said cathode, and a magnet providing magnetic lines of force directed along the axes of said control electrodes and acting to prevent electron current to said control electrodes for relatively high positive potentials thereon.

2. A controllable electron discharge tube comprising, a heated thermionic emissive cathode in the form of a filament bent into a circle complete except for a small separation at its ends to permit heating current to be conducted through the filament, a cylindrical control electrode concentrio with said cathode on an axis substantially at right angles to the plane of the cathode, said control electrode extending substantially the same distance in opposite directions from the plane of the cathode, an anode having surfaces on opposite sides of the plane of the cathode beyond the ends of the control electrode in planes substantially parallel with the plane of the cathode, and a permanent magnet providing a. magnetic field directed along the axis of said control electrode.

JAMES H. BURNETT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Gibson July 20, 1943 

